KernelCustomBuild
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| == Disclaimer == | The Kernel build documentation has moved to https://help.ubuntu.com/community/Kernel/Compile |
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| Building and using a custom kernel will make it very difficult to get support for your system. You will not be allowed to file bugs on the custom-built kernel (if you do, they will be Rejected without explanation). | Please update any bookmarks or links pointing to this page. |
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| If you have a commercial support contract with Ubuntu/Canonical, this will void such support. Also note that this page describes how to do things for the Edgy (2.6.17) kernel and newer! Until this kernel source, we did not have any mechanisms in place that would allow people to build their own kernels easily. This was intentional. This page does '''NOT''' describe how to build stock kernels from kernel.org. This is how to rebuild the actual Ubuntu kernel source. == Reasons for compiling a custom kernel == * You are a kernel developer. * You need the kernel compiled in a special way, that the official kernel is not compiled in (for example, with some experimental feature enabled). * You are attempting to debug a problem for which you have filed or will file a bug report on the stock Ubuntu kernel. == Reasons for NOT compiling a custom kernel == * You merely need to compile a special driver. For this, you only need to install the linux-headers packages. * You have no idea what you are doing, and if you break something, you'll need help fixing it. Depending on what you do wrong, you might end up having to reinstall your system from scratch. * You got to this page by mistake, but checked it out because it looked interesting. Believe me, this isn't interesting at all :) == What you'll need == To start, you will need to install a few packages. {{{ sudo apt-get install linux-kernel-devel fakeroot kernel-wedge kernel-package sudo apt-get build-dep linux-source }}} This will install the compiler related packages and kernel packaging tools. It will also install the git-core package, which is the best way to interact with the Ubuntu kernel source. == How to get the kernel source == There are two ways to obtain the Ubuntu kernel source. One is to use git (detailed instructions on it can be found in KernelGitGuide), which allows you to always stay in sync with the latest Ubuntu kernel source. The other way is to simply: {{{ apt-get source linux-source }}} Note that this will almost always be out of date compared to the latest development source, so you should use git if you need the latest patches. == Modifying the source for your needs == For most people, simply modifying the configs is enough. If you need to install a patch, read the instructions from the patch provider for how to apply. The stock Ubuntu configs are located in ''debian/config/ARCH/'' where ARCH is the architecture you are building for. In this directory are several files. The ''config'' file is the base for all targets in that architecture. Then there are several config.FLAVOUR files that contain options specific to that target. For example, here are the files for 2.6.17, i386: {{{ $ ls -l debian/config/i386/ total 88 -rw-r--r-- 1 me me 62737 Jun 14 18:31 config -rw-r--r-- 1 me me 1859 Jun 12 14:59 config.386 -rw-r--r-- 1 me me 1394 Jun 12 14:59 config.686 -rw-r--r-- 1 me me 1420 Jun 12 14:59 config.k7 -rw-r--r-- 1 me me 1519 Jun 12 14:59 config.server -rw-r--r-- 1 me me 1867 Jun 12 14:59 config.server-bigiron }}} If you need to change a config option, simply modify the file that contains the option. If you modify just the ''config'' file, it will affect all targets for this architecture. If you modify one of the target files, it only affects that target. Note: If you do not find the config files there, you may find them in your /boot directory. For instance: /boot/config-2.6.15-23-386 After applying a patch, or adjusting the configs, it is always best to regenerate the config files to ensure they are consistent. There is a helper command for this. To regenerate all architectures run: {{{ debian/rules updateconfigs }}} If you just want to update one architecture, run: {{{ debian/scripts/misc/oldconfig ARCH }}} == Building the kernel == To build the kernel(s) is very simple. Depending on your needs, you may want to build all the kernel targets, or just one specific to your system. However, you also want to make sure that you do not clash with the stock kernels. Use this command to build all targets for the architecture you are building on: {{{ AUTOBUILD=1 fakeroot debian/rules binary }}} The ''AUTOBUILD'' environment variable triggers special features in the kernel build. First, it skips normal ABI checks (ABI is the binary compatibility). It can do this because it also creates a unique ABI ID. If you used a git repo, this unique ID is generated from the git HEAD SHA. If not, it is generated from the uuidgen program (which means every time you execute the debian/rules build, the UUID will be different!). Your packages will be named using this ID. To build a specific target, use this command: {{{ AUTOBUILD=1 NOEXTRAS=1 fakeroot debian/rules binary-FLAVOUR }}} Where FLAVOUR is one of the main flavours of the kernel (e.g. generic) To build one of the custom flavours (found in debian/binary-custom.d/), use: {{{ AUTOBUILD=1 NOEXTRAS=1 fakeroot debian/rules binary-custom-FLAVOUR }}} As of this documentation, custom flavours include xen and rt. To trigger a rebuild, remove the appropriate stamp file from debian/stamps (e.g. stamp-build-server for the server flavour, etc.). The debs are placed in your kernel directory's parent directory. == Alternate Build Method: The Old-Fashioned Debian Way == The new Ubuntu build system is great for developers, for people who need the absolute latest bleeding-edge kernel, and people who need to build a diverse set of kernels (several "flavours"). However it can be a little complex for ordinary users. If you don't need the latest development sources, there is a simpler way to compile your kernel from the linux-source package. As suggested above, all you need for this is: {{{ sudo apt-get install linux-source mkdir ~/src cd ~/src tar xjvf /usr/src/linux-source-<version-number-here>.bz2 cd linux-source-<version-number-here> }}} Now you are in the top directory of a kernel source tree. Before building the kernel, you must configure it. If you wish to re-use the configuration of your currently-running kernel, start with {{{ cp -vi /boot/config-`uname -r` .config }}} Then, regardless of whether you're re-using existing configuration or starting from scratch: {{{ make menuconfig # or "xconfig" if you prefer }}} If you re-used the existing configuration, note that Ubuntu kernels build with debugging information on, which makes the resulting kernel modules (*.ko files) much larger than they would otherwise be. To turn this off, go into "Kernel hacking"; then, under "Kernel debugging", turn OFF "Compile the kernel with debug info". Now you can compile the kernel and create the packages: {{{ make-kpkg --rootcmd fakeroot --initrd --append-to-version=-some-string-here kernel-image kernel-headers }}} The packages should be placed in ~/. == When it's done == If you want to see the ubuntu splash screen (or use text mode) before you get to X instead of just a black screen, you'll want to make sure the framebuffer driver loads: {{{ echo vesafb | sudo tee -a /etc/initramfs-tools/modules echo fbcon | sudo tee -a /etc/initramfs-tools/modules }}} Now that you've told initramfs-tools what modules it should include and the build is complete, you can install the generated debs using dpkg: {{{ sudo dpkg -i linux-image-2.6.17-2-ef427c-k7_2.6.17-2.2_i386.deb sudo dpkg -i linux-headers--2.6.17-2-ef427c-k7_2.6.17-2.2_i386.deb }}} If you use modules from ''linux-restricted-modules'', you will need to recompile this against your new linux-headers package. Defails below. == Linux-Restricted-Modules: the Tough Stuff == The Linux-Restricted-Modules (l-r-m) package contains a number of non-DFSG-free drivers (as well as some firmware and the ipw3945 wireless networking daemon) which, in a perfect world, wouldn't have to be packaged separately, but which unfortunately are not available under a GPL-compatible license. If you use any of the hardware supported by the l-r-m package, you will likely find that your system does not work as well after switching to a custom kernel. In this case you should try to compile the l-r-m package. === Get the source === First, we make sure we have all the packages necessary to build l-r-m, and then we fetch the source: {{{ sudo apt-get build-dep linux-restricted-modules-2.6.some-version-ubuntu apt-get source linux-restricted-modules-2.6.some-version-ubuntu cd linux-restricted-modules-2.6.something }}} === Mess with debian/rules === Debian (and hence Ubuntu) packages are built by calling the the debian/rules script from the top source directory; this script is a specialized Makefile with 'targets' you can call as arguments when you run the script. The l-r-m debian/rules script is currently (2006-11) geared towards developers working with the official builds and makes certain assumptions about kernel version numbers and what header packages are installed; if you need to build l-r-m on your own, you will need to customize it. The full range of customizations are beyond the scope of this guide, but here are a couple examples of problems you're likely to run into and possible ways to solve them: '''Kernel Version Mismatch ''' If you built your kernel using one of the recommended methods, your kernel version is probably not precisely what debian/rules expects; for instance, my git-built kernel is called 2.6.19-7-ref-generic instead of 2.6.19-7-generic, while my make-kpkg-built kernel is called 2.6.19-7-suspend2-generic. You can solve this problem by changing this line (the actual value here will be different by the time you read this): {{{ abi_version = 7 }}} to something like this: {{{ abi_version = 7-ref }}} After making this change, the control file will have to be rebuilt by running: {{{ debian/rules debian/control }}} ''' Too Many Flavours ''' debian/rules expects you to have the header files for all possible kernel flavours already installed. If you only compiled one kernel flavour, this is of course impossible. So you need to look in debian/rules and change all the "flavours" lines so that only one flavour is listed -- the one you have already compiled. so for instance in my case, working on the i386 architecture: {{{ flavours := $(addprefix $(kernel_abi_version)-,generic, server, lowlatency) }}} became: {{{ flavours := $(addprefix $(kernel_abi_version)-,generic) }}} You may find that further modifications are necessary. ''' udebs mess you up ''' The standard "binary" target includes building udebs, which look for flavours that you may not have installed. I did two things: 1. Modified debian/d-i/kernel-versions.in 1. deleted "build-udebs" from the binary target I'm not sure the latter was necessary, but as you are not likely to need to build any udebs it's probably pretty safe to do. Now cross your fingers and hope! Try to build with: {{{ fakeroot debian/rules binary }}} I found that the system didn't recover very easily from errors and unsuccessful builds, and that the debian/rules "clean" target didn't always want to clean up, so I had to reinstall the source several times. It may be possible to redesign the debian/rules script to make it easier for non-devs to use. If I learn enough about Makefiles I will make an effort to do that... |
This page is now used for comments, questions and discussion. |
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| \!/ This page is duplicated on https://help.ubuntu.com/community/Kernel/Compile for some reason. Any changes here should be merged into that page, and this page should be deleted (redirected to the other) or provide additional information. Otherwise this will get even more messy over time. |
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| CategoryKernel CategoryDocumentation | CategoryKernel |
The Kernel build documentation has moved to https://help.ubuntu.com/community/Kernel/Compile
Please update any bookmarks or links pointing to this page.
This page is now used for comments, questions and discussion.
Comments
Q: What about custom install and netboot images (and their initrd etc)?, PeterMagnusson
A: Take a look at the Debian Installer instructions for this: http://wiki.debian.org/DebianInstaller/Modify/CustomKernel Although I haven't tried these instructions yet, and they might not quite work with the current Ubuntu Way, they look fairly comprehensive and should at least be a step in the right direction. (MatthewPalmer)
Q: What directory are you in when you run these commands ls -l debian/config/i386/ I'm sure you mean to untar the kernel source you just downloaded and cd into that tree (cd /usr/src ; tar xf linux-source-2.6.17.tar.bz2 ; cd linux-source-2.6.17) but there is no directory debian/config/i386 in there. debian/Config has .config files in it, but no bigiron file so i dono where that kernel comes from? EliCriffield
A: Maybe he meant debian/Config?
A2: On 6.06, the linux-source package does not include the debian directory, it seems. You need to install the source package for linux-image, with a command like
sudo apt-get source linux-image-2.6.15-27-386
Q: Is there any way to get a kernel build faster? I would like to do some "light" kernel hacking. What are the easy steps to just compile a kernel image?
- you can try using make-kpkg, the standard debian kernel-building tool. There are lots of guides around, hopefully the net person to read this page will have more time and put in a link.
Q: What is Ubuntu's default kernel config? The kernel doesn't put anything in /proc/config.
like all debian-based system, ubuntu's kernel puts the config in /boot/config-`uname -r`
Q: Maybe that's not the right place to ask, but I am stuck... I am trying to compile a vanilla kernel (to test an issue with suspend/resume). I do not want to use the make-kpkg method --- too slow on recompiles. So I can compile the kernel, install modules, and then I make the initrd.img with the update-initramfs thing... and all seems to work, but the new kernel simply boots on a BusyBox and does not boot the system. How do I build an initramfs image equivalent to the standard ubuntu one? RomanoGiannetti2
Well, auto-answering. update-initramfs do work. I was bitten by this bug:
http://lists.debian.org/debian-kernel/2006/07/msg00427.html which seems to still exists. Call update-initramfs with -v and it will fail.
Q: What is the correct way to add 'lib/firmware/<custom-kernel>' to a custom kernel .deb so that the kernel and firmware can be distributed together?
Q: Where do the firmware images from the generic kernel come from - (ie which package?) - or how does one get them so one can build a generic kernel? It would be useful if this was explained somewhere.
KernelCustomBuild (last edited 2011-03-13 19:14:33 by 84-73-137-162)